Fluid coupling devices such as rotary unions are used in industrial applications, for example, machining of metals or plastics, work holding, printing, plastic film manufacture, papermaking, semiconductor wafer manufacture, and other industrial processes that require a fluid medium to be transferred from a stationary source such as a pump or reservoir into a rotating element such as a machine tool spindle, work-piece clamping system, or rotating drums or cylinder. Often these applications require relatively high media pressures, flow rates, or high machine tool rotational speeds.
Rotary unions used in such applications convey fluid medium used by the equipment for cooling, heating, or for actuating one or more rotating elements. Typical fluid media include water-based liquids, hydraulic or cooling oils, and air. In certain instances, for example, when evacuating media from a fluid passage, rotary unions may operate under vacuum. Machines using rotary unions typically include precision components, such as bearings, gears, electrical components, and others, that are expensive and/or difficult to repair or replace during service. These components are often subject to corrosive environments or to damage if exposed to fluid leaking or venting from the rotary union during operation.
A rotary union typically includes a stationary member, sometimes referred to as the housing, which has an inlet port for receiving fluid medium. A non-rotating seal member is mounted within the housing. A rotating member, which is sometimes referred to as a rotor, includes a rotating seal member and an outlet port for delivering fluid to a rotating component. A seal surface of the non-rotating seal member is biased into fluid-tight engagement with the seal surface of the rotating seal member, generally by a spring, media pressure, or other method, thus enabling a seal to be formed between the rotating and non-rotating components of the union. The seal permits transfer of fluid medium through the union without significant leakage between the non-rotating and rotating portions. Fluid medium passing through the rotary union may lubricate the engaged seal surfaces to minimize wear of the seal members. When a rotary union is used with non-lubricating media (such as dry air) or without any media, the engaged seal surfaces can experience a “dry running” condition, which causes rapid seal wear due to lack of adequate lubrication. Extended periods of dry running can cause severe damage to the seal members, thereby requiring expensive and time-consuming replacement of one or both seal members.
High-speed machining equipment, such as computer-numerical-control (CNC) milling machines, drilling machines, turning machines, transfer lines, and so forth, use rotary unions to supply a medium directly to the cutting edge of a tool for cooling and lubrication in an arrangement that is commonly referred to as “through spindle coolant.” A through spindle coolant arrangement extends the service life of costly cutting tools, increases productivity by allowing higher cutting speeds, and flushes material chips that can damage the work-piece or cutting tool away from the cutting surfaces of the tool. Different work-piece materials typically require different media for optimal productivity and performance. For example, air or aerosol media may provide better thermal control when machining very hard materials, while liquid coolants may offer better performance when machining softer materials, such as aluminum. In addition, certain kinds of work may be performed more effectively and less expensively without a through-spindle medium.
In certain applications, it may also be desired to avoid any spillage of the working fluid of the coupling when the seal is disengaged, for example, when changing tool spindles. Along these same lines, it may further be desired to engage the rotary seal of the coupling before the working fluid is at full pressure so that the initiation of flow, which flow may include a mixture of the working fluid with air, does not cause leakage of the working fluid.